Switchable Metamaterials Research Articles

Switchable VO₂ Metamaterial Based on Planar and Vertical Split Ring Resonators for High-Performance Sensing

Switchable VO₂ Metamaterial Based on Planar and Vertical Split Ring Resonators for High-Performance Sensing

Ultra-broadband and thin switchable multifunctional metamaterial for terahertz wave

An ultra-broadband thin multi-functional and switchable metamaterial is examined in the terahertz (THz) regime. The proposed design achieved high polarization conversion efficiency and can be switched from a polarization converter to an absorber using the phase change transitioning of vanadium dioxide (VO2). The linear polarization conversion is achieved from 6.0 THz to 15.0 THz, achieving a bandwidth of 9.0 THz, and the absorption is realized from 5.0 THz to 16.0 THz with a bandwidth of 11.0 THz. These broadband characteristics were achieved by a simple metamaterial design incorporating a few layers. The relative bandwidth was 85% for the polarization conversion and 105% for the absorption. Moreover, the angular stability of the designed structure is impressive for various incident angles from 0° to 45°. The proposed switchable design has the potential to contribute to the development of tunable polarization rotating devices, on/off switching LPC devices, which have wide application potentials in THz detection, sensing, adaptive optics, and communications.

Optical terahertz metamaterial switch controlled via high-stability CsPbBr3 microcrystals

Dynamic control of terahertz metamaterials using thin organic perovskite active layers has been extensively researched. However, the preparation of organic perovskite devices requires strict environmental conditions, and the devices are prone to hydrolysis in air, which reduces performance. Herein, we report an optical terahertz metamaterial switch controlled via hybridization with high-stability CsPbBr3 microcrystals prepared through precipitation from a water–dimethylformamide (DMF) mixed-solution. Under light excitation, a modulation factor of 24% was achieved based on the photoelectric and photothermal effects of the CsPbBr3 microcrystals. After exposure to air for four months, the modulation factor remained essentially unchanged, demonstrating the exceptional stability of the system generated. Following the integration of CsPbBr3 microcrystals with the metamaterial, a frequency-shift of its dipole resonance and switching of Fano resonance was achieved, providing a novel approach to dynamic control of terahertz waves.

Tunable broadband absorption and broadband linear polarization converter based on vanadium dioxide

A composite dielectric metamaterial based on vanadium dioxide (VO2) is proposed to achieve flexible switching between two functions, broadband absorption, and polarization conversion, by adjusting the VO2 conductivity. The designed metamaterial functions as a broadband absorber when VO2 is in the metal phase. The absorber consists of a VO2 top structure, a silicon dioxide (SiO2) dielectric layer, and a VO2 thin film. Numerical simulation ns show that the absorber can absorb up to more than 90% in the frequency range of 3.22 ∼ 8.51 THz, and due to the symmetry of the structure, the absorber is characterized by polarization-insensitive properties and good absorption over a wider incidence angle. When VO2 is in the insulator phase, the designed metamaterial has a cross-polarization conversion function. The linear polarization converter primarily comprises an I-beam metal, a SiO2 dielectric layer, and a gold substrate layer. Numerical simulations demonstrate that the linear polarization converter accomplishes a line polarization conversion rate (PCR) greater than 90% within the 1.40 ∼ 4.11 THz frequency range, attains a close to 100% cross-polarization conversion rate (PCR) at 1.46, 1.95, 3.0, and 3.97 THz. To confirm the wave absorption mechanism of the absorber, we utilize the impedance matching theory to analyze it. The proposed switchable bifunctional metamaterials present significant potential for broader applications in future terahertz communication, imaging, stealth technology, and related fields.

Actively tunable and switchable terahertz metamaterials with multi-band perfect absorption and polarization conversion.

In this paper, we theoretically present and numerically demonstrate an actively tunable and switchable multi-functional metamaterial based on vanadium dioxide (VO2) and graphene in the terahertz region. When VO2 is in the metallic phase, the proposed metamaterial serves as a multi-band perfect absorber, which exhibits the characteristics of insensitive polarization and robust tolerance for variations of the incidence angle. When VO2 is in the insulator phase, the proposed metamaterial acts as a polarization converter, which can simultaneously achieve perfect linear-to-linear and linear-to-circular polarization conversions. The simulation results show the cross-polarization conversion rate can reach ∼100% at the frequency region from 6.09 to 6.43 THz as well as 8.15 THz. Moreover, the ellipticity of linear-to-circular polarization conversion reaches ±1 at frequencies of 5.75 and 8.34 THz, respectively, which means the linear polarization waves can be completely converted into circular polarization waves. The proposed metamaterial provides new insight for the design of optoelectronic devices with multi-functionality in the terahertz region.

Realization of bifunctional photothermal and radiative cooling based on self-adaptive VO2/PDMS metamaterial

The integration of photothermal (PT) and radiative cooling (RC) for sustainable energy collection has garnered much attention. In this work, a novel polydimethylsiloxane (PDMS) metamaterial is first developed to achieve an efficient radiative cooling. A high reflection of 91.57 % is obtained in the solar band. The average emissivity in the first and second atmospheric windows is up to 93.62 % and 85.58 %, respectively. It can be well explained through the analysis of the electromagnetic power loss. Subsequently, the phase change material of VO2 is deposited in the top PDMS interval to yield adaptive switching between the solar and infrared bands. The patterned VO2/PDMS metamaterial switches from RC mode to PT mode when the temperature exceeds 341 K. Unlike the previous work, this new bifunctional mode operates flexibly during the daytime upon the external thermal stimuli. Finally, the cooling power with different non-radiative heat transfer coefficients is systematically investigated. These numerical results indicate that our patterned PDMS/VO2 metamaterial has great potential in the field of temperature-adaptive switching between PT and RC modes, improving the utilization efficiency of energy in dynamic environments.

Impedance-Controllable Embedded Resonator for Switchable High-Selectivity Metamaterial Rasorber

A new technique for designing a dynamically controllable transparent window in the metamaterial absorber is investigated. Active lossy layer and lossless layer are proposed to establish the rasorber. First, the impedance-controllable embedded resonator is presented as a choke to limit the current flowing through the lossy elements. The interdigital and meander lines are applied to independently equivalent the large lumped capacitor and inductor required for low-frequency (L/S-band) resonance. It is demonstrated that the impedance loading of the inductive embedded resonator makes for a miniaturized unit size of 0.086 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda_{L}$</tex-math> </inline-formula> . Then, the cascaded embedded resonator on the lossless layer realizes a switchable high-selectivity passband in the reflection band. The transition from transmission band to absorption band is reduced due to the sharp roll-off edges of the passband. Finally, the rasorber prototype is fabricated and validated by the free-space measurement. By switching the bias of the p-i-n diodes, a high-selectivity window at 2.2 GHz can be triggered while it keeps absorbing in the whole band (1.2–3.7 GHz, 102%) at window-off state. Principles of operation and synthesis procedure are presented in this article.

Switchable metamaterials for broadband absorption and generation of vector beams

Metamaterial (MM) based on double-split resonator and vanadium dioxide (VO2) in terahertz (THz) region is proposed in this paper, which integrates broadband absorption (ABS) and generation of vector beams. Simulation results show that by tuning the VO2 into metallic phase, the ABS of proposed MMs achieves over 90% in 1.35–2.18 THz. The physical mechanism of broadband ABS is clarified by introducing the impedance matching theory and distributions of electric field. Moreover, ABS characteristics of the designed MMs at different polarization angles and incident angles are also studied, respectively. While VO2 is in insulated state, simulation results indicate that the radial polarized beam and the angular polarized beam can be generated when the incident wave is x-polarization and y-polarization, respectively. The polarization conversion rate over 90% is realized between 1.37 THz and 2.20 THz within the incident angle of 10°. The bi-functional MMs proposed in this paper has promising applications in modulators, imaging and sensors.

New metamaterial mathematical modeling of acoustic topological insulators via tunable underwater local resonance

This study presents a new type of active underwater local resonance metamaterial mathematical model for topologically protected acoustic wave propagation. The underwater acoustic metamaterial consists of arrays of core cylinders coated with soft shells periodically located in a water environment. An efficient but simple computational model is established to analytically predict the system band behavior. Compared to a system with only Bragg scatters, two double Dirac cones (DDCs) are observed in the dispersion curve due to the local resonance mechanism. The result obtained from numerical analysis shows great consistency with analytical prediction. By tuning structural parameters, the four-fold degeneracy is realized at the center of the irreducible Brillouin zone, i.e., the Γ point. It leads to the generation of two dipolar states and two quadrupolar states. Motivated by the theoretical prediction, locations of the cylinders are tuned and the closing-reopening phenomenon of bandgaps in both higher frequency region and lower region is observed with topologically protected phase transition. Besides, it is found that two frequency domains for topologically protected interface modes (TPIMs) occur. It provides potentials for two passive working frequency ranges without structural reconstruction or active tuning of the system. The effects of temperature on TPIM behavior are also demonstrated. Both working frequencies of TPIMs can be easily tuned to different ranges without influencing the quality of TPIMs. Besides, robustness and defect-immune properties of the topologically protected wave propagation are exhibited. With temperature control, this smart system can be performed as an acoustic metamaterial switch device.

Versatile polarization manipulation in vanadium dioxide-integrated terahertz metamaterial.

Broadband and switchable versatile polarization metamaterial is crucial in the applications of imaging, sensing and communication, especially in the terahertz frequency. Here, we investigated versatile polarization manipulation in a hybrid terahertz metamaterial with bilayer rectangular rods and a complementary vanadium dioxide (VO2) layer. The VO2 phase transition enables a flexible switching from dual-band asymmetric transmission to dual-band reflective half-wave plate. The full width half maximum (FWHM) bandwidths of dual-band asymmetric transmission are 0.77 and 0.21 THz, respectively. The polarization conversion ratio (PCR) of the reflective metamaterial is over 0.9 in the frequency ranges of 1.01-1.17 THz and 1.47-1.95 THz. Angular dependences of multiple polarization properties are studied. The proposed switchable polarization metamaterial is important to the development of multifunctional polarization devices and multichannel polarization detection.

Anisotropic Temporal Metasurfaces for Tunable Ultrafast Photoactive Switching Dynamics (Laser Photonics Rev. 15(10)/2021)

Switchable Metamaterial Devices In article number 2100244, Tian Jiang and co-workers report a novel polarization-coding all-optical metadevice with a temporal dynamic modulation feature. The switching dynamic can be alternated between a quasi-steady state with a recovery time larger than 2 ns and an ultrafast transient state with a recovery time less than 25 ps in two orthogonal polarization channels, which is believed to be a substantial advance in extending polarization multiplexing metadevices.

Achieving dual-band absorption and electromagnetically induced transparency in VO2 metamaterials

A new type of terahertz switchable metamaterial is proposed with dual functions. By introducing vanadium dioxide possessing insulator-to-metal transition, the designed metamaterial can be switched from a dual-band absorber to an analog of electromagnetically induced transparency. When vanadium dioxide is in the conducting state, the designed structure works as a dual-band absorber with 100% absorptance at 1.02 THz and 1.71 THz. When vanadium dioxide is in the insulating state, the designed structure works as an analog of electromagnetically induced transparency. The performances of bifunctionality are omnidirectional and efficient in the incident angle range of 60° or 30° in two modes. The proposed design may enable advanced applications in the fields of modulator and filter.

Temperature-dependent transformation multiphysics and ambient-adaptive multiphysical metamaterials

Temperature-dependent transformation thermotics provides a powerful tool for designing multifunctional, switchable, or intelligent metamaterials in diffusion systems. However, its extension to multiphysics lacks study, in which temperature dependence of intrinsic parameters is ubiquitous. Here, we theoretically establish a temperature-dependent transformation method for controlling multiphysics. Taking thermoelectric transport as a representative case, we analytically prove the form invariance of its temperature-dependent governing equations and definitively formulate the corresponding transformation rules. Finite-element simulations demonstrate solid and robust thermoelectric cloaking, concentrating, and rotating performance in temperature-dependent backgrounds. Two practical applications are further designed with temperature-dependent transformation: one is an ambient-responsive cloak-concentrator thermoelectric device that can switch between cloaking and concentrating; the other is an improved thermoelectric cloak with nearly thermostat performance inside. Our theoretical frameworks and application design may provide guidance for efficiently controlling temperature-related multiphysics and enlighten subsequent intelligent multiphysical metamaterial research.

Switchable bifunctional metamaterial for terahertz anomalous reflection and broadband absorption

A terahertz switchable metamaterial is proposed with bifunctional properties based on a mixed structure of graphene and vanadium dioxide (VO2). When VO2 is metal, this metamaterial can be used to perform the function of anomalous reflection. It is composed of VO2 blocks, topas spacer, and VO2 film. By adjusting the size of VO2 blocks, the gradient transformation is formed, so the normally incident beam is reflected to the left side at the angle of 38.4° at 3.0 THz. When VO2 is insulator, this design can be used to realize a broadband absorber. It has a broadband absorption with more than 90% absorptance in the range of 1.29–3.08 THz, and there are two absorption peaks with 99% absorptance at 1.545 THz and 2.55 THz. By adjusting Fermi energy level of graphene, intensity and bandwidth of broadband absorption can be dynamically changed. In addition, the designed metamaterial is insensitive to incident angle. Our design could be applied in many promising fields as intelligent absorption and terahertz switch.

Torsional bandgap switching in metamaterials with compression–torsion interacted origami resonators

Torsional vibrations are unavoidable in beam-type structures in various engineering practices, and the advent of metamaterials provides a solution through the generation of bandgaps. However, unlike their flexural counterparts, tunable torsional bandgaps are seldomly studied due to two major difficulties: the existing metamaterial's units are less torsional-sensitive and the reliable torsional sensing techniques for validations are less available. In this work, switchable torsional bandgaps are realized in a metamaterial beam with a bistable resonator design based on Kresling origami with attached eccentric balls. We find that, through compression–torsion interaction of the proposed origami resonators and the corresponding wave-coupling phenomenon, torsional bandgaps can be generated and efficiently tuned, which leads to lower and wider vibration isolation frequency zones. Thanks to bistability, Kresling resonators arranged with eccentric balls can achieve bandgap switching. Specifically, based on the compression–torsion interaction of the bistable Kresling origami, wave coupling will be weakened/enhanced when the Kresling resonators arranged with eccentric balls turn from the 1st/2nd state to the 2nd/1st state, and, thus, the switching of torsional bandgaps can be realized. In order to experimentally validate the tunable torsional bandgaps, a high-sensitive fiber Bragg grating (FBG) displacement sensing system containing two parallel FBG sensors is set up to extract the torsional responses. This research will be helpful for future studies focusing on regulating torsional waves through compression–torsion interaction and mode conversion utilizing wave coupling.

Cellular automata dynamics of nonlinear optical processes in a phase-change material

Changes in the arrangement of atoms in matter, known as structural phase transitions or phase changes, offer a remarkable range of opportunities in photonics. They are exploited in optical data storage and laser-based manufacturing, and have been explored as underpinning mechanisms for controlling laser dynamics, optical and plasmonic modulation, and low-energy switching in single nanoparticle devices and metamaterials. Comprehensive modeling of phase-change processes in photonics is, however, extremely challenging as it involves a number of entangled processes including atomic/molecular structural change, domain and crystallization dynamics, change of optical properties in inhomogeneous composite media, and the transport and dissipation of heat and light, which happen on time and length scales spanning several orders of magnitude. Here, for the first time, we show that the description of such complex nonlinear optical processes in phase-change materials can be reduced to a cellular automata model. Using the important example of a polymorphic gallium film, we show that a cellular model based on only a few independent and physically-interpretable parameters can reproduce the experimentally measured behaviors of gallium all-optical switches over a wide range of optical excitation regimes. The cellular automata methodology has considerable heuristic value for the study of complex nonlinear optical processes without the need to understand details of atomic dynamics, band structure, and energy conservation at the nanoscale.

Controllable Terahertz Switch Using Toroidal Dipolar Mode of a Metamaterial

We present a controllable terahertz (THz) metamaterial switch by manipulating toroidal dipolar mode in simulation. The metamaterial switch consists of periodically patterned metallic split rings with photosensitive silicon stripes. The excitation of toroidal dipolar resonance is closely dependent on the transition between the dielectric and conductive phases of photosensitive silicon. The toroidal dipolar mode is exploited to modulate the ON/OFF-switching transmission of THz wave under wide incident angles. The operation mechanism and frequency tunability are discussed.

Tunable plasmon induced transparency and multispectral transparency with large group delay in graphene metamaterials

Tunable plasmon included transparency (PIT) and multispectral transparency in the THz region have been achieved with graphene metamaterials, which consist of four graphene cut wires on the dielectric substrate. The PIT transparency window originates from the bright-bright mode coupling with two sets of identical graphene stips. The electric field distribution at each resonant peak is fully examined and the number of optical resonant peaks can be flexibly altered with the designed strip length. The transmission spectra agree well with the Lorentz fitting. Moreover, multispectral transparency can also be dynamically tuned via Fermi energy (E F). Namely, the resonant peaks move into the high frequency region with a larger E F. The dispersion behavior is explored elaborately and the group delay can reach up to 10.22 ps, which is one magnitude higher than the previous work. Finally, the movement of the multispectral transparency with different embedded solutions is fully examined in the application of sensing. Such active and switchable graphene metamaterials may open up a new avenue in the application of optical filters, switchers or sensors.

Folding at the Microscale: Enabling Multifunctional 3D Origami-Architected Metamaterials.

Mechanical metamaterials inspired by the Japanese art of paper folding have gained considerable attention because of their potential to yield deployable and highly tunable assemblies. The inherent foldability of origami structures enlarges the material design space with remarkable properties such as auxeticity and high deformation recoverability and deployability, the latter being key in applications where spatial constraints are pivotal. This work integrates the results of the design, 3D direct laser writing fabrication, and in situ scanning electron microscopic mechanical characterization of microscale origami metamaterials, based on the multimodal assembly of Miura-Ori tubes. The origami-architected metamaterials, achieved by means of microfabrication, display remarkable mechanical properties: stiffness and Poisson's ratio tunable anisotropy, large degree of shape recoverability, multistability, and even reversible auxeticity whereby the metamaterial switches Poisson's ratio sign during deformation. The findings here reported underscore the scalable and multifunctional nature of origami designs, and pave the way toward harnessing the power of origami engineering at small scales.

Switching between the Functions of Half-Wave Plate and Quarter-Wave Plate Simply by Using a Vanadium Dioxide Film in a Terahertz Metamaterial**Supported by the Scientific and Technological Developing Scheme of Jilin Province (Grant No. 20180101281JC), “135” Research Project of Education Bureau of Jilin Province (Grant No. JJKH20190579KJ), and “111” Project of China (Grant No. D17017).

We propose a switchable THz metamaterial that can be switched between two functions of half-wave plate and quarter-wave plate. The two switchable functions can be simply achieved by inserting a VO2 film in the metamaterial design. Finite-difference time-domain (FDTD) simulation results show that the proposed metamaterial can convert x-polarized incident wave to y-polarized reflected wave when VO2 is at metal phase, and convert x-polarized wave to circularly polarized wave when VO2 is at insulator phase. The metamaterial performs well in the two functions, i.e., the same broad working frequency band and near perfect polarization conversion. The switching effect originates from the switchable Fabry–Pérot cavity length induced by the phase change of VO2. We believe that our findings provide a reference in designing switchable metamaterials.